1. Field of the Invention
The present invention relates to an interface (electroencephalogram interface) system for allowing a device to be manipulated by utilizing an electroencephalogram.
2. Description of the Related Art
In recent years, wearable devices such as head-mount displays (hereinafter also referred to as “HMDs”) are gaining prevalence due to decreases in the size and weight of devices. Normally, as interfaces of devices, methods such as pressing a button, moving a cursor to make a decision, and manipulating a mouse while looking at a screen have been used. However, if the aforementioned physical device manipulations are required when manipulating a device whose body has a small size and which is characterized to be handsfree, e.g., an eyeglass-type HMD, the handsfree feature will be undermined, thus being ineffective. Therefore, attention is drawn to interfaces for easily controlling a device without performing any physical manipulations, specifically, interfaces utilizing an electroencephalogram that make it possible to quickly control a device by merely thinking.
An electroencephalogram is an encephalic activity (electrical activity of cranial nerve cells) measured as an electrical signal based on a difference in potential between a reference electrode and an measurement electrode. An example of an interface utilizing an electroencephalogram is a method and apparatus of determining a human psychological state and the like by utilizing an event-related potential which is described in Japanese Laid-Open Patent Publication No. 2005-34620 which is referred to as “Patent Document 1”. Patent Document 1 discloses a technique of determining an option which a user wishes to select by utilizing a characteristic signal of an event-related potential of his or her electroencephalogram.
Specifically, an electroencephalogram interface has been realized in which an electrode is worn on the parietal; words are randomly displayed on a screen; and a word which is selected by a user is determined by utilizing a positive component (P300 component) that appears in a time slot from 300 ms to 500 ms based on the timing of displaying the word which the user wishes to select as a starting point, for example.
In a conventional electroencephalogram measurement, electrodes are worn according to the position notation of the International 10-20 system, such that measurement is performed with a measurement electrode being worn on the head. In Patent Document 1, an electroencephalogram measurement is performed by using a characteristic signal at a Pz (median parietal) position or a Cz (median center) position according to the International 10-20 system. It is known that the characteristic signal utilized in Patent Document 1 is intensely measured at the location of the Pz position. Therefore, Pz is mainly used as an electrode position of conventional electroencephalogram interfaces.
However, generally speaking, an electroencephalogram measurement must be performed by using an electrode which is worn at the parietal as mentioned above. Therefore, in the case where a device which does not have a structure to come in contact with the parietal (e.g., the aforementioned HMD) is used, it is necessary for the electroencephalograph to have a shape extending across the head, as in a pair of overhead-type headphones. However, since there is a strong need for downsizing any wearable device to be worn on the face such as an HMD, it is highly likely that the portion extending across the head (as in headphones) will be considered unnecessary in the future. Moreover, a shape extending across the head is aesthetically poor, and may make the hair messy when worn, and thus is not an idealistic HMD shape of the future. Thus, it is a prerequisite for an HMD shape not to extend across the head.
In view of the above circumstances, in order to use an HMD-type device in combination with an electroencephalogram interface, it is necessary to separately wear an electrode for measuring an electroencephalogram at the parietal by some means, other than the HMD itself.
For example, Japanese Laid-Open Patent Publication No. 2004-16658, which is referred to as “Patent Document 2”, discloses a method in which each a plurality of corded electrodes included in an HMD is attached at a desired place (head) (FIG. 4).
However, an HMD is a device which is frequently put on or taken off, rather than being perpetually worn. Therefore, it will be a great burden on the user to have to separately wear a device in addition to the HMD.
In answer thereto, an example of performing an electroencephalogram measurement by placing electrodes within the range of an eyeglasses shape is disclosed in Japanese Laid-Open Utility Model Publication No. 6-70704 which is referred to as “Patent Document 3”. FIG. 24 shows the construction of a device for electroencephalogram electrode attachment which is disclosed in Patent Document 3. This device for electroencephalogram electrode attachment includes an elastic contact belt inside a C-shaped headband, such that electrodes which are placed on the contact belt enable electroencephalogram measurements. In accordance with this device for electroencephalogram electrode attachment, the electrodes are simultaneously worn when the device is worn, which eliminates the need to separately wear another device, so that the user's burden of device wearing is reduced.
However, when constructing an eyeglass-type electroencephalogram interface apparatus by using the construction of Patent Document 3, it is necessary to dispose an output section for presenting a visual stimulation at the position of a lens of the eyeglasses, so that the electrodes disposed on the face front are likely to be shifted. The reason is that the construction of Patent Document 3 supports the wearable device via support at the user's temples, which is achieved through clamping of the headband, and via support at the user's forehead, which is achieved through pressuring of the contact belt.
Any wearable device is supported by being pressed against a user. Therefore, if a video output device or the like is disposed at the position of a lens of the eyeglasses, an increased weight will act on the wearable device front, thus making it likely for the electrodes disposed on the contact belt (i.e., disposed at the face front) to be shifted in a downward direction.
In order to reduce shifting of the electrodes, the clamping of the headband or the pressuring of the contact belt may be increased in intensity. However, an increased pressuring on the user will lead to an increased burden on the user associated with clamping, which makes long hours of wearing difficult.